The distribution of intracellular alkali metals in Reference Man

A review of recent literature and a re-analysis of data used in Publication 23 of the International Commission on Radiological Protection (ICRP) have revealed several problems regarding the distribution of the predominantly intracellular alkali metals potassium, rubidium and caesium in ICRP Reference Man. In this paper we re-evaluate the distribution of the intracellular alkali metals in humans and we offer an approach for selecting reference concentrations for the organs of a typical adult human. For non-skeletal tissues, reference values for K, Rb and Cs are determined as a trimmed weighted mean of reported values remaining after studies involving apparently questionable populations or measurement techniques have been eliminated. The skeleton is treated as a special case, with explicit consideration being given to the heterogeneous distribution of these elements among different regions and different types of skeletal tissue. The most significant suggested changes for the intracellular alkali metals are for Rb in the skeleton and total body. ICRP Reference Man has a total Rb content of 0.68 g, compared with our estimate of only 0.25 g, and a skeletal Rb content of 0.21 g, compared with our estimate of only 0.013 g. This has important dosimetric implications for radiorubidium, because the retention model for Rb given in ICRP Publication 30 assigns a large portion of an intake to the skeleton on the basis of the large skeletal Rb content assigned to Reference Man in ICRP Publication 23.